For all those interested on why projects like X-33, Venturestar or any other SSTO (Single stage to Orbit) eventually fail in today's world without the use of Nuclear power from an engineering standpoint, I will direct you here:
The Cold Equations Of Spaceflight
The Freeper discusion on the topic:
The F-1 engine produced 1.7 million pounds of thrust, and the five-F1 Saturn V put circa 150 tons into orbit. This proposed booster would have five 1.2 million pound thrust engines, and would put over six times as much into orbit. This makes me a little curious, but I'd hazard a guess that the greater payload to orbit comes from dropping the weight of the Saturn V fuel components. (?)
seen it?
No one will ever let you launch a live nuke from the surface of Earth. It'd be dicey launching a cold space engine as a payload.
Outstanding! I like the idea of putting 1000 tons into orbit with every shot. The first 1000 tons could consist of several orbital tow/maintenance vehicles for repair/movement of satellites/stations/cargo.
It's an interesting design. It suffers from one main problem, mainly that, given currently forseeable technology, it won't work.
One problem stems from here:
"This engine produces 1,200,000 pounds of thrust, with an exhaust velocity of 30,000 meters per second, from a thermal output of approximately 80 gigawatts. This equates to an Isp of 3060 seconds. Several sources state that a gas core NTR can exceed 5000 seconds Isp, so 3060 is well inside the overall performance envelope. The three turbopumps from the SSME are run at low power levels, and even losing a pump allows the engine to continue running as long as there is no damage to the nuclear core."
The assumptions involved here are too broad and, frankly, wrong. To begin with the closed cycle (i.e. "lightbulb") GCNR variants tend to top out at 20,000 m/s exhaust velocity according to my research. Requiring 30,000 m/s calls for a very high-performance, and possibility of which is questionable.
But this is a mere quibble. Even with 20,000 m/s, performance is vastly increased over chemical boosters and the payload mass would simply need to be toned down. The main problem is in the next part.
"Lets assume this design is able to achieve a thrust to weight ratio of ten to one, so the engine and all of its safety systems, off-line fuel storage, etc, weighs 120,000 pounds. I think we can build this engine easily for 60 tons."
This estimate sounds reasonable, but is, in fact, quite wrong. Basic research would have determined this. The problem is not that closed-cycle GCNRs need be so massive, but rather that they suffer from poor mass flow. You can spit out that hydrogen at very high velocities, but you can't spit out very much of it per unit time. No proposed closed-cycle GCNR, to my knowledge, has achieved a thrust-to-weight ratio greater than one. Ten is completely out of the question. Alas, inspiring as this rocket is, it will never be able to lift itself off the ground.
But all hope is not lost. One possibility is to use an open-cycle GCNR. These benefit from higher exhaust velocities (50,000 m/s is frequently quoted) and higher thrust-to-weight ratios, though I'm not sure if they can achieve ten-to-one. These would probably allow for a rocket similar to the author's specifications to be constructed. The downside is that such a rocket releases its nuclear fuel to the environment at a steady rate. This doesn't particularly bother me, but it would be politically inconvenient. This is the reason that closed-cycle GCNRs were developed in the first place.
Another possibility is to use a solid-core nuclear thermal rocket, which the author briefly touched on but then abandoned in favor of the GCNR. The temperature limitations due to keeping the reactor solid only allow exhaust velocities of around 8000 m/s, but certain solid NTR designs such as the DUMBO type allow thrust-to-weight ratios as high as 70, comparable to a space shuttle main engine, and release no radioactive fuel. This may also allow a similar design.
Keep in mind that I'm only speaking to actual release of the fissionables and their byproducts. Even with a solid-core design, a nuclear rocket of any kind generates intense gamma and neutron radiation when critical. If the rocket carries crew or passengers, some amount of radiation shielding may be necessary. I'm not knowledgable enough about the subject to say how much, particularly given that the hydrogen fuel would absorb neutrons very efficiently, but it needs to be considered.
Alternatively, wait thirty to fifty years for a space elevator to be build, at which point surface-to-orbit rockets will be a moot point.
Anyway, though you'll never find a more adamant advocate of nuclear power and space exploration than me, but this particular design will not work. Sorry.
NASA Chief: Space Shuttle, Int'l Space Station Were Mistakes (Link Only)
USA Today | 27 Sep 2005 | Traci Watson
Posted on 09/28/2005 9:42:08 AM EDT by af_vet_rr
http://www.freerepublic.com/focus/news/1492795/posts
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